The invention relates to an excess pressure release for gas of the type described in the preamble to claim 1.
For securing palletized goods for instance in a container air cushions are placed and inflated in the gaps typically occurring between separate pallets and/or between the pallets and the walls of the container or another form of transport unit.
Each air cushion is filled manually with compressed air by means of a filler gun. This entails that the operator may unintentionally overfill the air cushion such that the goods are damaged or at worst the air cushion ruptures. Rupture of the air cushion during inflation thereof poses a risk to the safety of the operator. If the cushion ruptures in transit, the goods may be damaged.
Since the air cushion serves to slow down or to absorb any movements in the goods, the pressure in the air cushion increases or decreases according to the load to which the goods are subjected. It is thus not possible to provide the air cushion with a safety valve, which could reduce the pressure, if necessary, at excess pressure.
The applicant has carried out tests on the inflation of air cushions by means of various pressure-relief valves. Typically, the pressure in the air cushions has to be for instance 0.2 bar. Tests have shown that due to the poor flow in the pressure-relief valve it takes about 15 minutes to fill an air cushion by means of a pressure-relief valve set to 0.2 bar. If a pressure-relief valve is not used, it usually takes about 45 seconds to fill the air cushion, but this embodiment involves the above risk of an unintended rupture of the air cushion.
SE published specification No. 350.321 discloses a charging valve with built-in pressure relief, for instance for gas, having a biassed piston with a passage. A gas reservoir is filled through said piston until a predetermined pressure has been obtained. When this pressure has been reached, differences in area in the valve structure cause a differential pressure to urge the piston back against a spring power and lead the gas out to the surroundings through pressure relief openings. Consequently, the charging valve does not merely shut off the inlet pressure, when the gas reservoir has been charged to the desired pressure.
U.S. Pat. No. 5,462,081 discloses a self-regulating excess flow valve. In normal flow conditions the flow medium flows through a biassed piston. As the flow volume increases, the flow force urges the piston upwards and thus increases the area on which the flow medium exerts a pressure. As a result a drop of pressure occurs below the piston and the piston is spring-urged downwards again. Thus this valve does not serve to stop a charge when a specific pressure has been reached.
U.S. Pat. No. 5,215,113 discloses a safety shut-off valve for hydraulic systems. A valve housing is provided with a valve member with through-going passages abutting a spring. During normal operation the medium flows through these passages. When the pressure on the valve inside exceeds the spring power, the inside is urged forward and closes the passages and thus the flow therethrough. Thus it is not a question of ensuring a specific pressure on the discharge side of the valve.
U.S. Pat. No. 4,192,343 discloses a pressure-relief valve having a biassed hollow pilot piston. The pressure medium on the inlet side is effective on a small surface and moves a conical valve back against a spring force so as to open the valve. The medium may then flow past the conical valve head and exerts pressure on the upper face of the piston. Since the area of the upper face of the piston exceeds that of the valve inlet, the spring power of the piston is more easily overcome and the valve is more easily urged into its full-open position. As mentioned the valve in question is a pressure-relief valve and cannot be used to inflate air cushions, the valve controlling and relieving the pressure on the inlet side, while the pressure on the outlet side usually being atmospheric pressure.
The object of the invention is to inflate the air cushion quickly within about 45 seconds, while avoiding the said risk of unintentional overfilling and rupture of the air cushion.
According to the invention an excess pressure release of the above type is used instead of a pressure-relief valve for reducing the pressure to the desired about 0.2 bar, according to the invention said excess pressure release being adapted as stated in the characterising part of the claim 1.
The inlet port of the excess pressure release is connected to another type of pressure-relief valve rendering a pressure of for instance 6.0 bar, while the outlet port of the excess pressure release is connected to the air cushion to be inflated with air. An inflation valve of the type known from the applicant""s Danish patent application No. 1996 01148 may be provided in the air cushion. By connecting the air cushion with such an inflation valve the access from the excess pressure release to the air cushion is effected mechanically such that pressure is not required for opening the inflation valve. When a handle-operated air release valve (not shown) provided between the inlet port of the excess pressure release and the above pressure relief valve is opened, the pressure of the said for instance 6.0 bar instantaneously opens the excess pressure release against the force from the biassing means acting on the valve body such that the compressed air flows past the inlet valve seat and the adjacent outer end of the valve body, further in through the said openings in the periphery of the inlet end to the outlet passage provided in the outlet end of the valve body in the outlet port of the excess pressure release and further into the open inflation valve of the air cushion.
The air flows at great speed through the excess pressure release into the air cushion, which is filled within for instance 45 seconds. Due to the injector effect of the air current through the valve body to the outlet port of the excess pressure release, an underpressure arises which in turn via the connection of the outlet port with the other part of the valve chamber causes an underpressure in this part of the valve chamber acting to keep the valve open. When the pressure in the air cushion has reached the desired level of for instance 0.2 bar, a counter pressure arises in the outlet port and stops the injector effect, whereby the underpressure in the said other part of the valve chamber vanishes or changes to a slight over-pressure. Jointly with the over-pressure obtained in the other part of the valve chamber, the biassing means of the excess pressure release urges the valve body to adopt and maintain its closed position, whereby the excess pressure release is shut-off for additional gas supply. This action takes immediate effect when the air pressure in the air cushion has reached the desired over-pressure. As a result a fast and secure closure of the air supply is obtained. In order to ensure that the piston means dividing the valve chamber into two parts does not affect the closure, the said first part of the valve chamber communicates with the surroundings.
As stated in claim 2, preferably the opening between the second part of the valve chamber and the outlet port is obtained by providing the outlet end of the valve body with a conical shape as an injector nozzle, said outlet end jointly with the valve housing forming an annular access opening between the valve housing and said outlet end of the valve body.
Some air cushions are provided with a flexible non-return valve, the opening of which requiring force. Accordingly, the excess pressure release according to the invention may have mechanical means for urging the piston means into its open position as stated in claim 3 and said mechanical means may advantageously be formed as rendered in claim 4.